Method for removing polymer on surface of carbon nano tube

Abstract

The invention relates to a method for removing a polymer on the surface of a carbon nanotube. The method comprises the following steps: growing a germanium film on a carbon nanotube film on the surface of a substrate; carrying out annealing treatment on the substrate on which the germanium film and the carbon nanotube film are formed; and removing the germanium film by adopting hydrogen peroxide corrosion, and cleaning the substrate on which the carbon nanotube film is formed by adopting an organic solvent so as to remove the polymer on the surface of the carbon nanotube. According to the method provided by the invention, the damage to the carbon nano tube in the annealing process can be reduced, and the removal effect of the polymer on the surface of the carbon nano tube can be improved.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to a carbon nanotube film, and in particular, to a method for removing polymers on the surface of carbon nanotubes. Background Art

[0002] Semiconductor technology with silicon as the core material has promoted profound changes in human information society for more than half a century. However, as silicon-based devices gradually approach their physical and engineering limits, the global semiconductor industry is facing new challenges and opportunities in the post-Moore era. Although technologies such as strained silicon, high-k metal gate, and fin field-effect transistor (FinFET) have been adopted to continue the development trend of Moore's law, it has become increasingly difficult to further miniaturize silicon-based devices. Therefore, material innovation has become a key factor in the development of semiconductor technology. Among them, single-walled carbon nanotubes (SWCNTs) have attracted wide attention due to their many advantages such as high mobility, long mean free path, and ultrathin body, and have the potential to replace traditional semiconductor materials.

[0003] However, although the current solution-based purification and self-assembly technologies can prepare high-density, high-semiconductor-purity, and even chirality-enriched array carbon nanotube films, the organic polymers used in the process of purifying carbon nanotubes are also difficult to avoid remaining on the prepared carbon nanotube films. The presence of organic polymers will seriously affect the MOS interface of carbon nanotube devices and reduce the performance and reliability of the devices. Summary of the Invention

[0004] In view of this, in order to at least partially solve the above-mentioned technical problems, the present invention provides a method for removing polymers on the surface of carbon nanotubes.

[0005] According to an embodiment of one aspect of the present invention, a method for removing polymers on the surface of carbon nanotubes is provided, including:

[0006] Growing a germanium film on the carbon nanotube film on the surface of the substrate;

[0007] Annealing the substrate formed with the germanium film and the carbon nanotube film; and

[0008] Etching and removing the germanium film with hydrogen peroxide and cleaning the substrate formed with the carbon nanotube film with an organic solvent to remove the polymers on the surface of the carbon nanotubes.

[0009] According to the method for removing polymers on the surface of carbon nanotubes provided by the above embodiment of the present invention, by covering the carbon nanotube film with a germanium film, the damage to the carbon nanotubes caused by the annealing treatment can be reduced, the introduction of defects can be reduced, and thus the interfacial electrical properties of the carbon nanotubes and the field-effect transistors formed using the carbon nanotubes can be improved.

[0010] According to the method for removing the polymer on the surface of carbon nanotubes provided in the above embodiments of the present invention, compared with directly annealing in an air atmosphere, the germanium-coated annealing provided by the present invention has a better effect on removing the polymer on the surface of carbon nanotubes, and can almost completely remove the polymer in a shorter annealing time. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention and do not limit the present invention.

[0012] Figure 1 It is a flowchart of the method for removing the polymer on the surface of carbon nanotubes provided by the embodiment of the present invention;

[0013] Figure 2A It is a schematic cross-sectional view of the substrate provided by the embodiment of the present invention;

[0014] Figure 2B It is a schematic cross-sectional view of a carbon nanotube film formed on the substrate provided by the embodiment of the present invention;

[0015] Figure 2C It is a schematic cross-sectional view of a germanium film formed on the carbon nanotube film provided by the embodiment of the present invention;

[0016] Figure 2D It is a schematic cross-sectional view of the substrate with a carbon nanotube film formed thereon after cleaning provided by the embodiment of the present invention;

[0017] Figure 3 It is a Raman spectrum diagram of an untreated carbon nanotube film in the related art, a carbon nanotube film after removing the surface polymer provided by Embodiment 1 of the present invention, and a carbon nanotube film after annealing treatment provided by Comparative Example 1 under a laser with a wavelength of 532 nm; and

[0018] Figure 4 It is a Raman spectrum diagram of a carbon nanotube film after removing the surface polymer provided by Embodiment 2 of the present invention and a carbon nanotube film after annealing treatment provided by Comparative Example 2 under a laser with a wavelength of 325 nm.

[0019] DESCRIPTION OF REFERENCE NUMERALS:

[0020] 1 - Substrate;

[0021] 2 - Carbon nanotube film;

[0022] 3 - Germanium film;

[0023] 4 - Carbon nanotube film without polymer. DETAILED DESCRIPTION OF THE INVENTION

[0024] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings. However, the present invention can be implemented in different forms and should not be construed as limited to the embodiments presented herein. On the contrary, providing these embodiments will make the invention thorough and complete, and fully convey the scope of the present invention to those skilled in the art. In the drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated, and the same reference numerals denote the same elements throughout.

[0025] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprising", "including", etc. used herein indicate the presence of the described features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0026] In the related art, removing the polymer on the surface of carbon nanotubes has become the primary goal in the preparation of high-performance carbon nanotube metal-oxide-semiconductor devices (MOS devices). Currently, the most commonly used removal method is to directly anneal the carbon nanotube film to thermally decompose the polymer on the surface of the carbon nanotubes. However, the carbon nanotubes will also be damaged at the annealing temperature, introducing more defects and reducing the performance of the carbon nanotubes and the MOS devices using these carbon nanotubes.

[0027] In view of this, the present invention provides a method for removing the polymer on the surface of carbon nanotubes to reduce the damage to the carbon nanotubes during the annealing process and improve the removal effect of the polymer on the surface of the carbon nanotubes.

[0028] Figure 1 It is a flowchart of the method for removing the polymer on the surface of carbon nanotubes provided by the embodiment of the present invention.

[0029] According to an exemplary embodiment of the present invention, the present invention provides a method for removing the polymer on the surface of carbon nanotubes. Referring to Figure 1 as shown, it includes: step S01 to step S03.

[0030] Step S01, grow a germanium film on the carbon nanotube film on the surface of the substrate.

[0031] In the embodiment of the present invention, the material of the substrate 1 is not limited herein. The substrate 1 can be, for example, high-resistivity silicon.

[0032] Figure 2A It is a schematic cross-sectional view of the substrate provided by the embodiment of the present invention.

[0033] Figure 2B It is a schematic cross-sectional view of the substrate with a carbon nanotube film formed thereon provided by the embodiment of the present invention.

[0034] In an embodiment of the present invention, with reference to Figure 2A , Figure 2B as shown, the carbon nanotube film 2 is an array carbon nanotube film with a density of about 300 CNT / μm. The polymer on the surface of the carbon nanotube film 2 includes poly[9-(1-octylnonyl)-9H-carbazole] (PCz).

[0035] Figure 2C FIG. is a schematic cross-sectional view of a germanium film formed on the carbon nanotube film provided by the embodiment of the present invention.

[0036] In some embodiments, with reference to Figure 2C as shown, a germanium film 3 is grown on the carbon nanotube film 2 by electron beam evaporation or sputtering.

[0037] In some embodiments, the thickness of the germanium film is 1 to 100 nm. For example, it can be 1 nm, 10 nm, 20 nm, 50 nm, 100 nm, but is not limited to the listed values. If the thickness of the germanium film is too small, it is difficult to completely wrap the carbon nanotube film; if the thickness of the germanium film is too large, it will isolate the polymer on the surface of the carbon nanotube from the air, and the polymer cannot contact the oxygen in the air. Controlling the thickness of the germanium film within 1 to 100 nm can completely wrap the carbon nanotube film and enable the polymer to react with the oxygen in the air.

[0038] In an embodiment of the present invention, a germanium film 3 is grown on the carbon nanotube film by electron beam evaporation. The vacuum degree of the electron beam evaporation chamber is 5×10 -7 mbar, and the set power is 5%. The thickness of the grown germanium film can be about 6 nm, for example.

[0039] Step S02, annealing the substrate formed with the germanium film and the carbon nanotube film.

[0040] In some embodiments, the annealing temperature for the annealing treatment can be 200°C to 500°C. For example, it can be 200°C, 300°C, 400°C, 450°C, 500°C, but is not limited to the listed values.

[0041] In some embodiments, after reaching the annealing temperature, a heat preservation treatment is carried out; the constant temperature time for the heat preservation treatment is 10 s to 10 h. For example, it can be 10 s, 100 s, 1000 s, 1 h, 2 h, 3 h, 5 h, 10 h, but is not limited to the listed values. If the heat preservation time is too small (less than 10 s), it is difficult to completely remove the polymer; if the heat preservation time is too large (more than 10 h), the increase in the polymer removal rate with the increase in the heat preservation duration is not obvious; controlling the heat preservation time within the above range can effectively remove organic substances and save energy.

[0042] According to an embodiment of the present invention, the annealing atmosphere for annealing treatment includes any one of air, oxygen, argon, nitrogen, and reducing gas, and the reducing gas includes a mixed gas of nitrogen and argon.

[0043] Step S03, use hydrogen peroxide to etch and remove the germanium thin film and clean the substrate formed with the carbon nanotube thin film using an organic solvent.

[0044] In an embodiment of the present invention, a neutral hydrogen peroxide is used to etch and remove the germanium thin film, which has a relatively small impact on the carbon nanotubes. In some embodiments, the mass fraction of hydrogen peroxide is 0.01% - 10%, for example, it can be 0.01%, 0.1%, 1%, 5%, 10%, but is not limited to the listed values. The polymer on the surface of the germanium thin film 3 and the carbon nanotube thin film 2 has good adhesion, and the polymer adhered to the germanium thin film 3 can be removed simultaneously during the process of etching and removing the germanium thin film 3.

[0045] In some embodiments, the organic solvent includes one of isopropanol, acetone, ethanol, and N-methylpyrrolidone.

[0046] Figure 2D It is a schematic cross-sectional view of the substrate formed with the carbon nanotube thin film after cleaning provided by the embodiment of the present invention.

[0047] Reference Figure 2D As shown, after cleaning the substrate formed with the carbon nanotube thin film using an organic solvent, the polymer on the surfaces of the germanium thin film and the carbon nanotube thin film is removed, and a carbon nanotube thin film 4 without polymer is obtained.

[0048] The following schematically illustrates the method for removing the polymer on the surface of the carbon nanotubes. It should be noted that this example is only a specific embodiment of the present invention and does not limit the protection scope of the present invention.

[0049] Example 1

[0050] Step 1, use electron beam evaporation to grow a germanium thin film 3 on the carbon nanotube thin film 2 on the surface of the substrate 1.

[0051] Specifically, the substrate 1 is a high-resistance silicon, the carbon nanotube thin film 2 is an array carbon nanotube thin film with a density of about 300 CNT / μm, and the polymer on the surface of the carbon nanotube thin film 2 is poly[9-(1-octylnonyl)-9H-carbazole]. The vacuum degree of the electron beam evaporation chamber is 5×10 -7 mbar, the set power is 5%, and the thickness of the grown germanium thin film 3 is about 6 nm.

[0052] Step 2, use a tube furnace to perform annealing treatment on the substrate (sample) formed with the germanium thin film and the carbon nanotube thin film in an air atmosphere, including:

[0053] Place the sample to be annealed on a quartz tray, and place the quartz tray at the center of the heating zone of the quartz tube to ensure that the sample is heated evenly. Open the pressure relief valve of the vacuum system to place the sample under atmospheric pressure. Turn on the heater to slowly raise the temperature of the furnace tube of the quartz tube, and set the heating rate to 20 °C / min. When the temperature reaches 400 °C, maintain a constant temperature for 3 hours. After annealing is completed, turn off the heater to stop heating, and let the sample cool naturally in the tube. Wait until the temperature drops below 100 °C and then take out the sample to complete the annealing.

[0054] Step 3: Use hydrogen peroxide corrosion to remove the germanium film, and after soaking in isopropyl alcohol, obtain the cleaned carbon nanotube film 4 without polymers.

[0055] Specifically, put 198 ml of deionized water into a beaker; put 2 ml of 30% mass fraction hydrogen peroxide into the beaker, and stir the deionized water and hydrogen peroxide evenly, where the mass fraction of hydrogen peroxide is about 0.3%. Put the annealed sample into the beaker for 2 minutes to remove the germanium film, take out the sample and dry it with nitrogen; put the sample into 70 °C isopropyl alcohol and soak for 10 minutes, take out the sample and dry it with nitrogen.

[0056] Example 2

[0057] Use the same method as in Example 1 to remove the polymer on the surface of the carbon nanotubes. The difference is that the annealing temperature is 450 °C, and after reaching the annealing temperature, maintain a constant temperature for 15 minutes.

[0058] Comparative Example 1

[0059] Under an air atmosphere, use a tube annealing furnace to anneal the substrate with a carbon nanotube film formed on it. Specifically, place the substrate with a carbon nanotube film formed on it on a quartz tray, and then place the tray at the center of the heating zone of the quartz tube to ensure that the substrate with a carbon nanotube film formed on it is heated evenly. Open the pressure relief valve of the annealing furnace to place the substrate with a carbon nanotube film formed on it under atmospheric pressure; use the heater to slowly raise the temperature at a rate of 20 °C / min. When the temperature reaches 400 °C, maintain a constant temperature for 3 hours. Turn off the heater to stop heating, and let the substrate with a carbon nanotube film formed on it cool naturally in the quartz tube. Wait until the temperature drops below 100 °C and then take out the substrate with a carbon nanotube film formed on it to complete the annealing.

[0060] Put the substrate with a carbon nanotube film formed on it into 70 °C isopropyl alcohol and soak for 10 minutes, take out the substrate with a carbon nanotube film formed on it and dry it with nitrogen to obtain the cleaned carbon nanotube film.

[0061] Comparative Example 2

[0062] The polymer on the surface of the carbon nanotubes was removed by the same method as in Comparative Example 1. The difference was that the annealing temperature was 450° C., and after reaching the annealing temperature, the constant temperature was maintained for 15 minutes.

[0063] Figure 3 The Raman spectra of the untreated carbon nanotube film in the related art, the carbon nanotube film after removing the surface polymer provided in Example 1 of the present invention, and the carbon nanotube film after annealing provided in Comparative Example 1 under a laser wavelength of 532 nm are shown respectively. Figure 3 The abscissa represents the Raman shift, Figure 3 The ordinate represents the Raman intensity.

[0064] refer to Figure 3 As shown, the peak ratios of the G peak to the D peak of the untreated carbon nanotube film, the annealed carbon nanotube film provided in Comparative Example 1, and the carbon nanotube film after the surface polymer is removed provided in Example 1 of the present invention are 40.17, 9.62, and 59.68, respectively. Figure 3 It can be seen that the untreated carbon nanotube film has a Raman shift of 1620 cm -1 There is a PCz polymer absorption peak (polymer peak) nearby, indicating that there are polymer PCz residues on the surface of the carbon nanotubes. After the annealing treatment of Example 1 and Comparative Example 1, the PCz polymer absorption peak disappears, indicating that the polymer PCz on the surface of the carbon nanotubes has been effectively removed. However, after the air annealing of Comparative Example 1, the carbon nanotubes were severely damaged, and the peak ratio of the G peak to the D peak dropped significantly. After the treatment by the method of Example 1 of the present invention, the peak ratio of the G peak to the D peak did not decrease. The G / D peak ratio of the carbon nanotubes after annealing at 400°C in air atmosphere for 3 hours can reach 59.68, which fully demonstrates the significant effect of the present invention in protecting carbon nanotubes in the process of removing surface polymers, and can explain that the carbon nanotubes of the present invention have fewer defects on the surface.

[0065] Figure 4 The Raman spectra of the carbon nanotube film after removing the surface polymer provided in Example 2 of the present invention and the carbon nanotube film after annealing provided in Comparative Example 2 under 325nm laser, respectively. Figure 4 The abscissa represents the Raman shift, Figure 4 The ordinate represents the Raman intensity.

[0066] Under the 532 nm wavelength laser, the carbon nanotubes are fully excited and less affected by impurities, so a more accurate G / D peak ratio can be obtained to evaluate the defect level of the carbon nanotubes. However, when the polymer residue is less, it is difficult to observe the polymer peak. Since the absorption peak of the polymer PCz remaining in the sample is about 380 nm, Raman spectroscopy under a 325 nm laser closer to its absorption wavelength was used to further evaluate the polymer residue. From Figure 4 it can be seen that after the annealing treatment at 450 °C for 10 minutes in an air atmosphere in Example 2, almost no polymer absorption peak can be detected, while in Comparative Example 2, an obvious polymer absorption peak can still be observed after annealing and cleaning under the same conditions. That is to say, under the same treatment time, the polymer removal rate of Example 2 of the present invention is higher, which shows that the method of the present invention has a better effect on removing the polymer on the surface of carbon nanotubes.

[0067] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for removing polymers from the surface of carbon nanotubes, characterized in that: include: growing a germanium film on the carbon nanotube film on the surface of the substrate; performing annealing treatment on the substrate on which the germanium thin film and the carbon nanotube thin film are formed; as well as The germanium film is removed by etching with hydrogen peroxide, and the substrate formed with the carbon nanotube film is cleaned by an organic solvent to remove the polymer on the surface of the carbon nanotube.

2. The method according to claim 1, characterized in that The thickness of the germanium film is 1-100 nm.

3. The method according to claim 1, characterized in that The growth method of the germanium thin film includes one of an electron beam evaporation method and a sputtering method.

4. The method according to claim 1, characterized in that: The annealing temperature for the annealing treatment is 200°C to 500°C.

5. The method according to claim 1 or 4, characterized in that: After reaching the annealing temperature, heat preservation treatment is performed; The constant temperature time of the insulation treatment is 10s~10h.

6. The method according to claim 1, characterized in that The annealing atmosphere for the annealing treatment includes one of air, oxygen, argon, nitrogen and a reducing gas, wherein the reducing gas includes a mixed gas of hydrogen and argon.

7. The method according to claim 1, characterized in that The mass fraction of hydrogen peroxide is 0.01%~10%.

8. The method according to claim 1, characterized in that The organic solvent includes one of isopropyl alcohol, acetone, ethanol and N-methylpyrrolidone.

9. The method according to claim 1, characterized in that: The polymer includes poly[9-(1-octylnonyl)-9H-carbazole].

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